Lightly-sweet and chocolatey, Thomas Keller's rich cocoa brownies (Ad Hoc) are an indulgent treat. As per the original recipe, the brownie mix can be prepared up to a week ahead and stored in the refrigerator until ready to bake. Adapted, in language and procedure, from Thomas Keller, Ad Hoc At Home
Butter a 9-inch baking pan and line with parchment, leaving a 2-inch overhang on two sides of the pan. Lightly butter the parchment.**
In a medium bowl, sift together the flour, cocoa powder, and salt. Set aside.
Melt half of the butter (1-1/2 sticks) in the microwave or a small saucepan on the stove. Place the remaining 1-1/2 sticks of butter in a medium bowl and pour melted butter over them, stirring until almost all of the butter is melted. The mixture will become creamy in appearance. Stir in vanilla extract.
In a stand mixer fitted with the paddle attachment, beat the eggs and sugar on medium speed until thick and pale in color. With the mixer on low speed, add the sifted cocoa mixture and melted butter in three additions each, alternating between the wet and dry ingredients. Remove bowl from stand mixer and fold in chocolate chips with a rubber spatula or wooden spoon.
Spread the batter into the prepared pan and bake for 40-45 minutes, until a cake tester inserted into the center of the pan comes out clean (a few moist crumbs are okay). If the tester emerges coated, test again, as you might've inserted it into a pocket of melted chocolate.
Remove pan to a wire rack and cool 20 minutes. Using parchment overhang, remove brownies from pan to a cutting board and slice into 16 squares, or 12 rectangles. Dust with powdered sugar and serve slightly warm.***
*The original recipe calls for a block of chocolate, cut into chip-sized pieces. Each time I've made this recipe, I've used quality chocolate chips with excellent results.**Thomas Keller uses a 9-inch silicone baking mold. If using silicone, there's no need to butter the mold and line with parchment. Brownies baked in a metal or glass pan will have crisper edge pieces.***For the best texture, it's important to not over-bake the brownies. Baking until the tester is totally clean in the center will result in dry brownies.